The real problems with TSV-based devices are cost and production issues, thereby keeping the introduction of these products a moving target. CMOS image sensors based on TSVs appear to be in the market today, but complex memory and related products built around the technology are not expected to ramp until 2010, according to memory giant Samsung Electronics Co. Ltd.

Don't expect a 3-D device with memory and a processor until 2015, according to Samsung. Heat dissipation is the main problem with this type of device.

Meanwhile, at the International Solid-State Circuits Conference (ISSCC) here, Samsung described an 8-gigabit DDR3 DRAM, based on TSVs. TSV is a radical step up from today's chip-stacking technologies, such as wire-bonding, flip-chip, multichip packaging (MCP) and system-in-package. Experts define a true 3-D package as one that stacks various chips vertically and then connects them by deploying TSVs or related techniques. The aim is to shorten the interconnections between the chips, reduce die sizes and boost device bandwidths.

At ISSCCC, Samsung described a DDR3 DRAM based on 50-nm technology. Measuring 10.9- x 9-mm², the prototype device supports or stacks 4 devices, with a single master IC and three slave chips connected using 300 TSVs. The master is a 2-Gbit x 4 DDR3 DRAM with additional multi-rank control circuits, while the slaves have 2-Gbit memory cores.

The pitch of the TSVs are 80-mm, said Uksong Kang, principal engineer within the Memory Division at Samsung. ''The master acts as a buffer that isolates the channel and the slave chips,'' Kang said in the paper. ''This allows the I/O data rate to increase to 1600Mb/s.''

TSVs add latency of one clock cycle at 1333-Mb/s, according to Samsung. The device has a local and global datapath, a repair scheme and a power-noise reduction technology. The local datapath is bidirectional (read/write shared), while the global datapath is unidirectional (read/write separated).

Ground noise is rated as high as 350-mV when the TSVs are placed in the middle. Ground noise is rated at 100-mV when the TSVs are placed with power edge pads.